The present invention relates generally to polycrystalline cutter elements and more particularly to stud-mounted polycrystalline cutter elements with an improved stud-polycrystalline interface.
An abrasive particle compact is a polycrystalline mass of abrasive particles, such as diamond and/or cubic boron nitride, bonded together to form an integral, tough, high-strength mass. Such components can be bonded together in a particle-to-particle self-bonded relationship, by means of a bonding medium disposed between the particles, or by combinations thereof. For example, see U.S. Pat. Nos. 3,136,615, 3,141,746, and 3,233,988. A supported abrasive particle compact, herein termed a composite compact, is an abrasive particle compact which is bonded to a substrate material, such as cemented tungsten carbide. Compacts of this type are described, for example, in U.S. Pat. Nos. 3,743,489, 3,745,623, and 3,767,371. The bond to the support can be formed either during or subsequent to the formation of the abrasive particle compact.
Composite compacts have found special utility as cutting elements in drill bits. Drill bits for use in rock drilling, machining of wear resistant materials, and other operations which require high abrasion resistance or wear resistance generally consist of a plurality of polycrystalline abrasive cutting elements fixed in a holder. Particularly, U.S. Pat. Nos. 4,109,737 and 5,379,854, describe drill bits with a tungsten carbide stud (substrate) having a polycrystalline diamond compact on the outer surface of the cutting element. A plurality of these cutting elements then are mounted generally by interference fit into recesses into the crown of a drill bit, such as a rotary drill bit. These drill bits generally have means for providing water cooling or other cooling fluids to the interface between the drill crown and the substance being drilled during drilling operations. Generally, the cutting element comprises an elongated pin of a metal carbide (stud) which may be either sintered or cemented carbide (such as tungsten carbide) with an abrasive particle compact (e.g., polycrystalline diamond) at one end of the pin for form a composite compact.
Polycrystalline diamond (PCD) is used routinely as an abrasive wear and impact resistant surface in drilling, mining, or woodworking applications. The PCD typically is bonded to a metal stud which frequently exhibits ridges, circles, or other undulating features on the surface bonded to the PCD. These interfacial designs are an attempt to improve the adhesion of the PCD to the metal stud. Common failure modes of cutters are abrasive wear of the PCD; impact damage of the PCD caused by loads either parallel or perpendicular to the PCD carbide interface, i.e., percussion or shear damage, slowly propagating fatigue fractures either in the PCD or metal stud or at their interface, and thermal fractures.
Prior proposals aimed at improving the metal carbide stud-polycrystalline abrasive interface include U.S. Pat. No. 5,379,854 which proposes a cutter element whose end bears a plurality of ridges wherein each ridge has substantially planar top surface. U.S. Pat. No. 5,711,702 provides a carbide stud having a series of annual grooves of varying depth and to which a polycrystalline abrasive layer is attached. U.S. Pat. No. 5,355,969 provides a cylindrical composite compact where the interface is formed from a series of undulations. While these designs do provide increased surface area between the carbide stud and the polycrystalline abrasive cap, manufacturing of such studs often requires machining in the early stages of manufacturing and planar groove tops often leads to non-uniform or incomplete abrasive compacting between the ridges.